Find the local maximum and minimum values and saddle point(s) of the function. If you have three-dimensional graphing software, graph the function with a domain and viewpoint that reveal all the important aspects of the function. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.)
$f(x, y) = x^2 + y^2 - 3x^2 - 9y^2 - 9x$
local maximum value(s)
local minimum value(s)
saddle point(s) \qquad (x, y, f) =